My car it comes on if it drops below 40. Usually 37-38. In our Jetta V it comes on exactly ata 37 degreese, and flashes the temp with a snowflake on the computer LCD no less than 7 times and beeps 3 times. The beetle, by comparison, is a silent alerter
It should go back off onces it gets to 41, but it can stick. Nothing like freeze warning in summer!